1. Field of the Invention
The present invention relates generally to microwave and millimeterwave scanned antennas.
2. Description of the Related Art
There is a growing commercial demand for low-cost radar systems. For example, investigators around the world are working on the development of obstacle-avoidance radar systems for use in motor vehicles, e.g., automobiles, trucks, boats, military vehicles and aircraft. A key element of these radar systems is an antenna that can radiate a scanned microwave beam. Obstacles that are interrogated by the scanned beam cause an echo which is received by the antenna and sent to an electronic portion of the radar for processing.
For a collision-avoidance radar to be commercially viable, its elements, such as the scanned antenna, must be light weight, low cost, spatially compact and offer efficient performance with low maintenance costs over a long lifetime (e.g., &gt;10 years). In addition, the scanned antenna should preferably be based on manufacturing technologies that are well developed so as to reduce technical and schedule risks.
Prior art apparatus for scanning an antenna beam have generally fallen into two groups, mechanically-scanned antennas and electronically-scanned antennas. Gimbal systems have been extensively used in aircraft to facilitate the mechanical scanning of fixed-beam antennas. However, gimbal systems are typically heavy and costly to fabricate and usually require considerable maintenance.
In one exemplary type of electronically-scanned, movable waveguide vanes vary the phase of radiation through waveguide slots (e.g., see Markus, John, et al., McGraw-Hill Electroncis Dictionary, McGraw-Hill, New York, 5th Edition, 1994, p. 390). These systems involve a large number of moving parts so that both fabrication and maintenance costs tend to be high.
In another exemplary type of electronically-scanned, a plurality of phase shifters, e.g., ferrite and electronic, provide beam steering (e.g., see Stimson, George W., Introduction to Airborne Radar, Hughes Aircraft Company, El Segundo, 1983, pp. 577-580). Phased arrays can achieve high-speed scanning but the phase shifters and associated parts, e.g., waveguide networks and amplifiers, result in complex fabrication and high parts count.